1. Field of the Invention
This invention relates to thin film magnetic write head fabrication, in particular to the fabrication of such a write head that minimizes thermal pole-tip protrusion with a coil configuration that provides low power consumption for a given yoke length.
2. Description of the Related Art
Thin film induction-type magnetic write heads are used to encode magnetically stored information on moving magnetic media such as tapes and discs. In the simplest terms, such a head consists of two pole pieces separated at the air-bearing surface (ABS) by a narrow gap (the write gap) and yoked together behind the ABS to form an approximately horseshoe-shaped assembly. A conductive coil is patterned between the pole pieces which, when electrically energized, induces a magnetic field between the poles that fringes across the gap. It is this induced field that encodes small magnetic regions in the moving medium. In the most general terms, the performance of such a write head is related to its magneto-motive force (MMF), which is itself proportional to the product of the current in the coil and the number of coil turns. To improve write head performance, therefore, either the current or the number of coil turns (or both) must be increased. On the other hand, the power consumption and, therefore, the Joule heating of the head is proportional to I2R (current squared times coil resistance). If write head performance is to be improved by increasing the current, there will be a large corresponding increase in heating and the problem of thermal protrusion of the pole tip. Thermal tip protrusion is a major problem since the write head must be positioned increasingly close to the medium surface as written densities become greater. The challenge in writer design, therefore, is how to make a writer with a greater number of coil turns, while keeping the total coil resistance low and maintaining the same length of the yoke.
Chesnutt et al. (U.S. Pat. No. 6,356,410) teach a write head formation wherein an upper pole tip is formed on a write gap which is on a lower pole tip, and the upper pole tip comprises two layers, the lower of which is narrower than the upper. A schematic diagram of the write head also discloses a double layer of coils, formed one above the other and positioned above the upper pole tip and write gap.
Crue, Jr., et al. (U.S. Pat. No. 6,400,526) provide a write head and an associated preamplifier chip wherein the impedances of the two are matched to allow closer placement of the chip to the write head. The write head incorporates a write gap layer that separates the first pole pedestal (on the lower pole) from the second pole tip portion (on the upper pole) at the air-bearing surface (ABS) and then extends from the ABS to the back gap of the yoke formation. The write gap also separates the turns of the first coil layer from those of the second coil layer. It is noted that this configuration makes for a shorter yoke length and reduced flux rise time.
Santini (U.S. Pat. No. 6,339,523) teaches a method of constructing a merged read/write head wherein the write head is constructed before the read head. This reversed order of construction eliminates some problems associated with prior art merged read/write heads such as write gap curvature, damage to read element during fabrication of the write element and shorting of lead layer to shield layer.
Hong et al. (U.S. Pat. No. 6,178,070) teaches a method of forming more coils in a write head (as many as three layers) without the necessity of increasing the yoke height. The method involves forming a first coil layer within a first insulation layer between the upper and lower pole pieces. In the prior art write head, the first coil layer is formed on an upper surface of this first insulation layer, rather than within it.
With the exception of the method of Hong et al., cited above, the prior art does not teach specifically a method of improving the magneto-motive force of a write head while retaining its general structure and dimensions. Hong et al. address the problem by forming more coils within the body of the head. The present invention will treat the problem by retaining the same number of coils and a two coil structure, but will decrease the resistance of the coils and thereby allow a decrease in the power consumption and Joule heating of the write head.